| Objective: ||Develop a 20 dBi directive antenna for operation in an anechoic chamber.
|| Description: ||Typical aircraft communication systems use line-of-sight (LOS) antennas to provide the radio frequency (RF)links for air-to-ground and air-to-air. The patterns and gain of these antennas need to be measured individually, and more importantly, while installed on the aircraft. Open-air range testing can be performed to determine that, overall, the communication system is working properly but these tests do not provide a complete characterization of the radiation pattern produced by the antennas. This can lead to unacceptable performance in certain instances.
In order to fully evaluate the system to determine the envelope of operation, the installed antenna patterns must be measured. As the frequency of operation is reduced the size of the test antennas is increased. Most antenna ranges and anechoic chambers use log-periodic antennas to measure the radiation patterns and gain of the antennas under test.
The maximum gain of a antenna is simply defined as the product of the directivity and the efficiency. When the reference is a lossless isotropic antenna, the gain is expressed in dB of improvement over an isotropic radiator (DBi). An isotropic radiator is an antenna that radiates equally in all directions. The log-periodic antennas produce a realistic gain of about 6 dBi and produce beamwidths so wide that in many cases this causes excessive measurement error.
Accurate measurements at low frequencies in anechoic chambers suffer from multi-path reflections from the walls, ceiling, and floor even though they are covered with radar absorbing material. One way to reduce these effects is to use a highly directive test antenna with low sidelobes and a front-to-back radiation pattern ratio of greater than 20 dB.
There is a real need for a relatively small antenna that produces a directivity of 20 dB and operates from 100 to 300 MHz. Because of the limited space inside an anechoic chamber, the antenna size needs to be limited to 10 feet by 10 feet by 10 feet and weigh no more than 300 lbs. The small, low-frequency antenna needs to be easy to mount and align, to provide maximum utility in an anechoic chamber. The antenna should be linearly polarized and have the ability to either switch between vertical and horizontal polarizations or have the ability to easily, and remotely, rotate 90 degrees while mounted on the standing fixture. The cross-polarized E-field component of the linearly polarized antenna should be at least 20 dB below the co-polarized E-field component.
|| ||PHASE I: Design and model an antenna capable of meeting the qualifications and design a prototype that can be built and demonstrated during Phase II.
|| || ||PHASE II: Using the design from Phase I, build two prototype antennas and demonstrate the gains and polarization by measuring the patterns in a chamber.
|| ||DUAL USE COMMERCIALIZATION: Military application: Both commercial and military: This antenna can be used for chamber testing and communications applications where antenna size is critical, and may translate to other frequency bands. Commercial application: Both commercial and military: This antenna can be used for chamber testing and communications applications where antenna size is critical, and may translate to other frequency bands.
|| References: ||1. RAWCON 2000 Proceedings Page 33 “A New Wireless Network for 5 GHz License Exempt Applications”
2. Proceedings of the IEEE 1998 International Conference on Universal Personal Communications 5-9 October 1998 Volume 1 Pages 445-449 “Highly Structured Rosette Antenna Arrays for Wireless Multimedia Systems”, J. Sydor, J.Duggan.
3. Proceedings of the 20th Biennial Symposium on Communications, Queens University 28-31 May 2000, Queens University, Kingston Ontario. “Co-Channel Interference in Rosette Microcell Configurations” S.Gulder, J. Duggan.
4. Supergain antennas and the Yagi and circular arrays King, R.W.P.; Antennas and Propagation, IEEE Transactions on Volume 37, Issue 2, Feb. 1989 Page(s):178 - 186
5. A high gain YBCO antenna array with integrated feed and balun, Ivrissimtzis, L.P.; Lancaster, M.J.; Alford, N.McN.; Applied Superconductivity, IEEE Transactions on Volume 5, Issue 2, Part 3, Jun 1995 Page(s):3199 - 3202
|Keywords: ||Supergain, super directive antenna, anechoic chamber, log-periodic antennas, frequency of operation, radiation patterns, sidelobes, mutli-path, narrow beamwidth|